Method of winding helices



Aug. 24, 1965 R. G. Voss METHOD OF WINDING HELICES Filed Nov. 5. 1959 2 f a A /NVENTOR Akal/OSS By v ATTO/QN VA the helix.

United States Patent O 3,201,849 METHGD F WiNDlNG HEMCES Robert G. Voss, Westfield, NJ., assigner to Bell Telephone Laboratories, incorporated, New York, NY., a corporation of New York Filed Nov. 3, i959, Ser. No. 856,731 6 Claims. (Cl. 29-1555) This invention relates to helix fabrication techniques, and, more particularly, to the fabrication of helical transmission lines for use in electron discharge devices of the traveling wave tube type.

In devices of the traveling Wave tube type, broad band amplification at exceedingly high frequencies is achieved through the interaction of an electron beam and an electromagnetic wave traveling in synchronism along an extended path. inasmuch as the normal velocity of an electromagnetic wave is of the order of the speed of light, while that of an electron beam is of the order of onetenth to one-fifteenth of that speed, to achieve synchronism it is necessary that the velocity of the electromagnetic wave be decreased to that of the beam. One of the most useful arrangements for achieving this slowing down of the wave is a helical transmission line which surrounds the electron beam and along which the wave propagates. Usually a plurality of cylindrical support rods of any suitable insulator material which will not inthe proper pitch, but also to minimize the possibility of pitch variations during and after the winding process. Pitch variations, in addition to reducing the amount of gain obtainable, also give rise to reflections which, in tun produce signal distortion, and in more serious cases, self oscillation.

Heretofore, it has been the practice to wind a helix of a material such as molybdenum tightly on a mandrel of a rigid material such as tungsten and then to normalize The normalizing serves to relieve the stresses in the helix wire which were created during the winding, and, when these stresses are relieved, the helix wire relaxes, thereby providing suihcient clearance between the helix and the mandrel to permit withdrawing the mandrel. Prior to withdrawing the mandrel, but subsequent to the normalizing, the dielectric support rods are glazed to the helix in the manner, for example, taught in US. Patent 2,790,926 to I. A. Morton. While such a method produces helices of sufficient uniformity for low frequency applications, it has been found that for the very high fre uenc a nlications, where the helix size is uite small, there are non-uniformities in pitch produced which materially degrade tube performance. The non-uniformi- Vties arise in the normalizing step, when the helix wire relaxes or springs back, since it is no longer tightly bound to the mandrel. On the other hand, this helix spring back has heretofore been necessary to provide the clearance needed for withdrawing the mandrel.

clearance between the mandrel and the helix.

ICC

It is a further object of this invention to produce a rigidly mounted, uniform helix which retains its uniformity throughout its useful life.

These and other objects are accomplished by the method of the present invention which comprises the steps of coating the winding mandrel with a material which preferably hardens in air, winding the helix on the mandrel thus coated with sufficient tension to imbed the helix wire in the coating material, placing dielectric support rods prior-ly coated with a glazing material in Contact with the helix, and introducing the assembly into a furnace for glazing the rods to the helix.

ln accordance with the present invention, as the helix is wound the :iaterial with which the mandrel is coated acts to grip the helix Wire so that there is no slippage. This material is chosen from materials which will volatilize or, more specifically, burn olf under proper furnace conditions of heat and atmosphere. The glazing material is chosen to have a melting point slightly higher than the burning or oxidizing point of the mandrel coat-ing. Under these conditions, as the mandrel coating material commences to burn olf, a temperature has been reached where the glazing material has commenced to grip the helix. Thus there is a smooth transition from the helix being held by the coating material to the helix being held by the glazing material, and helix spring back is avoided. in addition, after the coating material has burned off, there is then suicient clearance for the mandrel to be withdrawn.

Accordingly, it is a feature of this invention that the process of winding a helix include the initial step of coating the mandrel with a thin layer of volatilizable or oxidizable material.

lt is another feature of the present invention that the material burns or oxidizes at a temperature near the melting temperature of the glazing material on the dielectric rods. v

it is still another feature ofthe present invention that the furnace atmosphere be such as to insure substantially complete burning off of the material with which the helix is coated.

lt is a further feature of the invention that the thickness of the layer on the mandrel be sufticient to insure clearance between the helix and mandrel after the material has burned off.

These and other'ieatures of the present invention will be more readily appreciate from the following description, taken in conjunction with the accompanying drawings, in which: Y

' PEG. l is a perspective View of an arrangement for accomplishing the first step of the invention; i

FlG. 2 is a cross-sectional view of a helix mandrel after spraying;

FIG. 3 is a partially sectional view of the assembly of elements prior to introduction into a furnace; `and FG. 4 is a partially sectional view of the elements after removal from the furnace.

Turning now to the drawings, there is disclosed in FIG. l a perspective view of one specific arrangement for accomplishing the rst step of the process of the present invention. A' plurality of mandrels il upon which the helices are to be wound are mounted between a rst support member StZ and a second support member i3. Advantageously, one of the support members such as member l2 contains a drive unit for rotating each of the mandrels lll about the mandrel axis. Support member i3 is so designed to permit the mandrels to turn about their axis while affording support for them. Mounted adjacent the supporting arrangement for the mandrels is a spray gun of any suitable, commercially available V11 is a substantially solid, hard `coating.r

Ain one winding operation.

;troduced into a controlled atmosphere furnace, notshown. .In a `preferred embodiment of the invention the" coating Y .material 22 initially comprised,a-s'olution of colloidal? .graphite in water, which on air-hardening became a layer -screw 18. Spray gun 14 is supplied with a suitable rnaterial for spraying the mandrels, the composition of which will be discussed more'fully hereinafter, through a sup; In addition,.the gun is supplied with 'Y vcompressed air for accomplishing the spraying function through a suitable supply conduit 21. Advantageously,

ply conduit 19.

spray gun 14 hasV an adjustable nozzle 22 for controllingy the rate of spraying and consequently the rate ofV deposimandrels 11 are caused to rotateabout their axes 'by means of the drive mechanism in support member 12. Initially the spray gun is at the limit of its travel in the direction of'support member 12.y The spray gun 14 vis Gun 14 is preferablyr mounted on `a carriage 16 Y tion of material on the mandrels 11. In operation, the f the dielectric rods 26- are preglazed, such as an alsimag glaze having a melting temperature in the order of 1100 degrees to 1200 degrees C., the glazing material -will have become tacky at 1000 degrees C. and will grip the helix. As a consequence, when the assembly of elements as de- ,V picted in FIG'. 3 is introduced into the furnace and the Vvtemperature of the furnace is raised, the coating 22 does rnot commenceY to burn oit until 'the glazing materialen the rods 26 has commenced to grip and adheretothe Vturns of the helix 23. As 1000 degrees C. is reached the coating 22 completely burns off'whilethe helix is p revented from moving or shifting by virtue of thegripping action of the glazing material.

In FIG. 4 the assembly of FIG'. y3 is depicted after the coating 22 is burned off. It can be seen from FIG. 4 that the glazing material on therods26V hasvmelted` sufficiently y to form fillets 27, which adhere irrnly to the turns of the 'actuated and concurrently therewith lead screwlt starts ,i

'to'rotate, causing gun 14 to move alongmandrels 11 toward support member 13. AIn this Vmanner a uniform coating is supplied to the mandrels 11, and any desired rthickness of coating, rthe significance of which will be discussed more fully hereinafter, may be vattained by ad- `justing the rate of spray, thel rate of translationalv movement of the gun 14 and the rate of rotation of mandrels Y In FIG. 2 there is .shown a .cross-sectional view of a mandrel 11 after sprayingrhaving a layer 22 of sprayed material thereon; As was pointed `out in the foregoing, the sprayed material whichris'necessarily in suspension' to permit spraying, is such that it preferably vair-hardens `after thespraying process, and the layerZZ" Turning now to FIG. 3, there is shown partially in the tension of the helix is`maintainedsuchV that the helix wireirnbedsitself intothe coatingmaterial 22, as best f coating material,. as is shown in FIG; 3,. In forder Vthat '.helix and,.,as,a consequence,jprevent any-rotational movement of'thehelix after winding. Preferably-'although not necessarily, the distance between the flat portions 24 onl the mandrel 11 is slightly greater than the' desired length of helix, and; there may be several'hat portions with, in. Y.

effect, several, helices of the desired vlength being` wound' After the helix has Abeen Woun placed in contact with the outsideofrthe turns'of theV helix. In general, there will-be three such support rods so placed; .however for Vsimplicity only one has been shown on mandrel d on the mandrel and rmly gripped inv placerby the actionof ,the ats 24 and lthe material 22, preglazed-dielectric supportrods 26are cross section the'assembly of elements as exists afterV vthe secondandthird stepsof` the process have been performed. Mandrel 11 with its coating 22 has wound therev ."on under tension a helix 23. During the winding processl i seen in the cross-sectional portionV of FIG.V3.vr Under. 'Y 'ideal conditions, it is preferred thatl the helix'wirefimbed 1 itself approximately half way into the'thickness' of the l the helix23 will be securely held in place 'on the mandreL; 'mandrel 1 1is supplied with hat portions 24 over which the helix is wound. The iiat po'rtions'actto'v distort the -helix thereby rigidly joining the helix to the. rods. In addition, it can be. seen. from FIG. 4 thatwith the removal of the coating 22 there is left a clearance between Vthe mandrel 11 and the helix'23, which clearance is sufcient to permit withdrawal of the mandrel after the helix has Vbeen cut to proper length. From the foregoing, it lcan readily be seenthat from the time the helix was rst wound` upon Vthe mandrel until the completion of the heating process the helix was held firmly andV constrained against any movement whatsoever, Viirstby the` gripping action aflordedby thev coating v22 ,withy the helix turns ,imbedded therein and inally-byqvthe gripping action of "the glazing material on the rods 2.6,.A The transition from the gripping action of the coating 22 'to the gripping action of the glazing material is made smoothly with no possible movement of the helixV being permitted.Vv As a consequence, the uniformity ofthe helix is limited only by the uniformityof the winding mechanism and there are'no non-uniformities introduced subsequent tothe winding step.' An additional advantage of the method of thepresent invention is'rthe fact thattheffurnace temperatures maybe vvsuch as to-normalize theV helix, there- 4by relievingstressesl without permitting spring back of the helix. Y .v f a In one helix windingoperationv embodying the principles 'of the present invention, a tungsten winding mandrel '.of,approximate1y .0375 inch diameter had-applied thereto ra coating of raquadag which was lapprbximately .00035 inch thick. The helix was then wound on the mandrel,

lthe helix wire diameter `beingapproximately-1.005 inch,

v and thewirewas imbedded in thel aquadag Vcoating to a ',fdepth offapproximately .00015 inch, leaving afthickness of coating between the surface ofthe mandreland theI wire'of approximately .0002 inch. The assembly was introduced into afurnace having an atmosphereof wet `forrning'gas of 8.5 percent nitrogen and 15 percent hydrogenandheated forthirty minutes in the furnace, with .in FIG. 3. Any suitablemeans may be used for holding the support rods in place against the helix turns.

With the elements thusy assembled, the assemblyis vin of graphite 22 on the Vmandrel 11. I have found that ifv vthe Vatmosphere of theifurnace comprises a wet forming gas, such as 8S percent nitrogen and l5percent Yhydro- C. By properly choosing the glazing material with which the maximum Vtemperature thereof beingV 1185 degrees C.

When-the helix wasfwithdrawn'from; the furnace the coating material was completely burned oil or lvolatili'zed and the helix Ywas firmly glazed toA the support rods26.

With the coating material' eliminated, Vtheinner diameter of the helix vwas approximately.'.0004 inch greaterthan the outer diameter of the mandrel, givingsufcient clear- 'ance for withdrawal of the helix from the mandrel.

While the particular materials and temperatures herein (disclosed have been found to work quite well in practice,

.it'is ,to be understood that! they are given here by way ofillust'ration ofthe principles of the-invention.l Numerousother materials and temperatures might lbe used by persons skilled jin the art without departing from the spirit .andscope ofthe present invention. For example,

' materials other than aquadag may be kusedfor Acoating the mandrel, in which case the furnace atmosphere may l Q be different in.order.to=assur 'co l t l t'l' gen, bubbled or passed through distilled water, thefgraph- Y e mp e e V0 a 1 Iza/Hon of ite coating 22 will burn'off at approximately 1000 degrees ,the coating material, andthe furnace temperaturesl may be somewhat different.`

AIn additionpwhile.dielectric support' rods have been shown, other types of support members may be used, even in some cases, the glass envelope of the tube itself.

What is claimed is:

1. A process for winding a wire helix comprising the steps of spraying a mandrel upon which the helix is to be wound with a colloidal suspension of graphite in water, letting the coating thus sprayed harden, winding the helix under tension on said mandrel whereby the turns of the helix become imbedded in said coating to a depth of approximately half the thickness of said coating, placing preglazed support rods in contact with the helix thus wound the glaze material on said support rods having a melting point such that it becomes tacky at the temperature at which the graphite coating burns off, and introducing the mandrel, the helix and the support rods thus assembled into a furnace having an atmosphere of wet forming gas and heating the assembly until the coating on said mandrel substantially completely burns off and the glazing material on the support rods adheres to the helix, cooling the assembly, and withdrawing the mandrel from the helix.

2. The method of fabricating helical slow wave circuits for traveling Wave tubes comprising the steps of winding a wire helix under tension around a mandrel having a coating thereon so as partially to imbed the wire helix into the coating, placing a preglazed support member adjacent the helix, and then heating the mandrel, helix and support member in an oxidizing inhibiting atmosphere to a temperature so that the coating on said mandrel burns olf substantially simultaneously with the glaze becoming at least tacky enough to grip the helix and prevent changes in the helix position.

3. The method of fabricating helical slow wave circuits for traveling wave tubes comprising the steps of winding a wire helix under tension around a mandrel having a colloidal graphite coating thereon so as partially to imbed the wire helix into the coating, placing a plurality of preglazed support rods adjacent the helix, and then heating the mandrel, helix and support member in a furnace having an oxidizing inhibiting atmosphere to a temperature and under such atmospheric conditions that there is a smooth transition between the helix being held by the coating and being held by the glaze as the coating substantially completely burns off and the glaze melts around the turns of the helix.

4. A process for winding helices for traveling wave tubes comprising the steps of spraying the mandrel upon which the helix is to be wound with a coating of air-hardening, thermally oxidizable material, winding the helix under tension on said mandrel whereby the turns of the helix become partially imbedded in said coating, placing a support member having glazable material in contact with the helix thus wound, said glazable material having a melting point such that it becomes tacky at the temperature at which said oxidizable material burns olf, said temperature being substantially higher than the operating temperature of the traveling wave tube, introducing the mandrel, the helix and the support member thus assembled in a controlled atmosphere furnace and heating the assembly until the coating on said mandrel substantially completely burns off and the glazing material of the support member grips the helix, cooling the assembly, and withdrawing the mandrel from the helix.

5. A process for winding a wire helix comprising the steps of spraying a mandrel upon which the helix is to be wound with a colloidal suspension of graphite in water, letting the coating thus sprayed harden, winding the helix under tension on said mandrel whereby the terms of the helix become partially imbedded in the coating, placing preglazed support rods in contact with the helix thus wound, the glaze material on said support rods having a melting point such that it becomes tacky at the temperature at which the graphite coating burns otf, introducing the mandrel, the helix and the support rods thus assembled into a furnace having an atmosphere of wet forming gas comprising a mixture of hydrogen and oxygen, heating the assembly until the coating on the mandrel substantially completely burns oil. and the glazing material on the support rods adheres to the helix, cooling the assembly, and withdrawing the mandrel from the helix.

6. A process in accordance with claim 5 wherein the helix support rods and mandrel are heated to a temperature of between 1100 degrees and 1200 degrees C.

References Cited by the Examiner UNITED STATES PATENTS 2,459,605 1/ 49 Warnken.

2,522,731 9/ 5 0 Wheeler 331-31 2,626,371 1/53 Barnett.

2,683,833 7/54 Zaphiropoulos 14C-71.5 X 2,812,499 11/57 Robertson.

2,894,223 7/59 Sinclair 333-31 2,903,657 9/59 Eichin.

WHITMORE A. WILTZ, Primary Examiner.

ARTHUR M. HORTON, WILLIAM W. DYER, JR.,

JOHN F. CAMPBELL, Examiners. 

1. A PROCESS FOR WINDING A WIRE HELIX COMPRISING THE STEPS OF SPRAYING A MANDREL UPON WHICH THE HELIX IS TO BE WOUND WITH A COLLOIDAL SUSPENSION OF GRAPHITE IN WATER, LETTING THE COATING THUS SPRAYED HARDEN, WINDING THE HELIX UNDER TENSION ON SAID MANDREL WHEREBY THE TURNS OF THE HELIX BECOME IMBEDDED IN SAID COATING TO A DEPTH OF APPROXIMATELY HALF THE THICKNESS OF SAID COATING, PLACING PREGLAZED SUPPORT RODS IN CONTACT WITH THE HELIX THUS WOUND THE GLAZE MATERIAL ON SAID SUPPORT RODS HAVING A MELTING POINT SUCH THAT IT BECOMES TACKY AT THE TELPERATURE AT WHICH THE GRAPHITE COATING BURNS OFF, AND INTRODUCING THE MANDREL, THE HELIX AND THE SUPPORT RODS THUS ASSEMBLED INTO A FURNACE HAVING AN ATMOSPHERE OF WET FORMING GAS AND HEATING THE ASSEMBLY UNTIL THE COATING ON SAID MANDREL SUBSTANTIALLY COMPLETELY BURNS OFF AND THE GLAZING MATERIAL ON THE SUPPORT RODS ADHERES TO THE HELIX, COOLING THE ASSEMBLY, AND WITHDRAWING THE MANDREL FROM THE HELIX. 